The present invention generally relates to medical devices useful in reducing and preventing spinal injury in patients with spinal trauma or patients undergoing aortic surgery. More specifically, the invention provides devices for insertion into the subarachnoid space for circulating and cooling the cerebral spinal fluid below body temperature. The flow rate of the cerebral spinal fluid is variably adjusted according to the pressure and temperature, respectively measured by a manometer and thermometer.
Spinal ischemia resulting in neurological complications occurs in patients sustaining a traumatic injury to the spinal cord or patients undergoing aortic surgery. Spinal cord injury can be classified as penetrating or blunt. In penetrating injuries, such as stab wound or gun shot wound to the spinal cord, complete severing of the spinal cord can occur, resulting in total muscular paralysis and loss of sensation below the level of injury. This condition of flaccid paralysis and suppression of all reflex activity following immediately upon transection of the spinal cord and involving all segments below the lesion is referred to as spinal shock. In most cases, reflex activity returns within 1 to 6 weeks from the onset of the spinal shock. Once transection of the spinal cord has occurred, peripheral reinnervation by the nervous system does not occur.
Spinal shock also occurs in blunt injuries, such as in motor vehicle accident, where compression of the spinal cord by impingement from fractured or dislocated vertebral bodies results in sensory and motor impairment below the level of cord involvement. Diagnosis of spinal fracture or dislocation is often made on X-rays. Spinal cord compression can be diagnosed on MRI, CT scan with myelogram, or lumbar puncture (Queckenstedt test). The mechanism of spinal ischemia is mostly caused by swelling of the cord. In these patients, hypotension may also occur as a result of loss of vascular sympathetic tone in the involved area. Urinary and/or bowel incontinence is a common complication due to impaired autonomic function.
Spinal ischemia is also a common postoperative complication following aortic surgeries, such as abdominal aortic aneurysmectomy. The incidence of spinal cord ischemia/stroke during aortic surgery is typically over 10%. During abdominal aortic aneurysm (AAA) repair, for example, the spinal arteries, which provide blood supply to the spinal cord, are often severed from the diseased aorta, and some but not all of which are later resutured to the prosthetic graft. As a result, blood flow to the spinal cord is reduced. When reduction of spinal perfusion lasts the duration of the surgery, typically more than forty-five minutes, spinal ischemia/stroke may ensue, often resulting in anterior spinal artery syndrome. The classic syndrome is characterized by paraplegia, rectal and urinary incontinence, loss of pain and temperature sensation, but with sparing of vibration and proprioceptive sense. Patients may also sustain neurologic deficits in the lower extremities after abdominal aortic surgery due to loss of posterior column modalities.
Brain damage associated with either stroke or head trauma is worsened by hyperthermia and improved with hypothermia. Current treatment for acute ischemic stroke and head injury is mainly supportive. A thrombolytic agent, e.g., tissue plasminogen activator (t-PA), can be administered to stroke patients who have no contraindication to t-PA. Current treatment for patients suffering from spinal injury is also supportive, e.g., to secure local hemostasis and to prevent infection by appropriate debridement, closure, and administration of antibiotics in penetrating spinal injury. In patients suffering from blunt injuries, surgical decompression of the spinal cord may be performed to restore neurological function. Spinal ischemia/stroke due to aortic surgery is also treated with supportive therapy, e.g., maintaining hemodynamic stability and monitoring neurological status, while waiting for the neurological deficits to recover with time. Therefore, besides surgical intervention in blunt injury, there is currently no good treatment which reduces neurologic damage to the spinal cord.
New devices and methods are thus needed in treating spinal ischemia/stroke in patients having spinal cord trauma or aortic surgery, in preventing spinal ischemia in patients anticipating a major thoracoabdominal surgery, or in cerebral ischemia, which minimizes neurological complication and improves the patients"" quality of life without causing significant side effects.
The invention provides devices and methods for reducing neurologic complications in patients sustaining trauma to the spinal cord or undergoing aortic surgery. More specifically, the invention provides devices and methods for cooling the cerebral spinal fluid (CSF) surrounding the spinal cord.
A first embodiment of the device comprises two elongate catheters, each having a proximal end, a distal end, and a lumen communicating with a port at the distal end. The distal ends of the first catheter and the second catheter are adapted for insertion into a patient""s subarachnoid space. The proximal ends of the catheters are connected to a pump to facilitate circulation of the CSF through the lumens of the catheters. A refrigeration system is connected to the pump to provide adjustable cooling of the CSF, such that CSF flowing through the lumen of the first catheter is cooled to below body temperature before flowing into the lumen of the second catheter. The CSF pressure in the circuit is measured by a manometer included in the catheters, the pump, or the refrigeration system. It will be understood that although the pump is advantageous, it may not be included in all embodiments for circulation of the CSF.
In another embodiment, the distal end of each catheter carries a needle which facilitates introduction of the devices into the subarachnoid space. A suture flange is mounted on a distal region of the first catheter and/or the second catheter for securing the devices after insertion into the subarachnoid space. Other embodiments of the devices include radiopaque markers mounted at the distal end of each catheter for identifying the position of the catheters in the subarachnoid space.
In still another embodiment, the proximal end of each catheter includes a port for infusing fluid, such as Ringer""s lactate solution, or pharmaceutical agents into the subarachnoid space. The port can be used to drain the CSF for reducing pressure in the subarachnoid space. Alternatively, a release valve may be included proximally in one of the catheters to drain the CSF when the pressure exceeds a desired threshold. A distal region of each catheter may be angled relative to the proximal end to facilitate entry and rostral advancement in the subarachnoid space.
In still another embodiment, the devices include at least one thermometer. The thermometer can be included in the proximal end of the first and/or second catheter for measuring the temperature of the CSF or CSF/fluid mixture entering and exiting the subarachnoid space.
The methods for cooling the spinal cord to prevent neurologic damage during inadequate spinal perfusion utilize the devices disclosed herein. In a first method, the distal end of the first catheter is inserted percutaneously between the spinous processes of lumbar vertebrae L3 and L4 or L4 and L5 into the subarachnoid space. The distal end of the second catheter is inserted in the lumbar region at a level above or below the insertion of the first catheter. The second catheter is advanced rostrally in the subarachnoid space so that the distal port is positioned preferably in the low cervical or high thoracic region of the spine or optionally in the lumbar region. The position of the catheters can be verified under fluoroscopy in the embodiments where the distal ends of the catheters include one or more radiopaque marker. Preferably, the CSF is aspirated from the first catheter, cooled by the refrigeration system, and passed into the second catheter. Alternatively, the CSF is aspirated from the second catheter, cooled by the refrigeration system, and passed into the first catheter. In this manner, the CSF is cooled to below normal body temperature, which can be monitored by thermometers included in either or both catheters. The greater the cooling the greater the degree of protection is likely for the spinal cord.
In another method, after insertion of the catheters, the CSF is drained in the lumbar region to reduce the CSF pressure to zero. The CSF pressure can be monitored by a manometer included in either or both catheters. The CSF is collected in a bag and discarded after the procedure. Fluid, such as Ringer""s lactate, is infused through one of the catheters, preferably the second catheter, and drained passively through the first catheter. The CSF collected in a bag may be discarded or reintroduced at the end of the procedure. The CSF/Ringer""s lactate mixture is cooled through the refrigeration system and circulated by activating the pump. The pump can be either volume limited or pressure limited. The temperature of the CSF mixture can be reduced rapidly, and the flow rate is adjusted to maintain the desired temperature. The CSF pressure is maintained preferably at a minimum, i.e., at approximately zero, to maximize perfusion to the spinal cord.
In still another embodiment, a port protecting mechanism, e.g., a net or a fence guard, is mounted at the distal ends of the catheters. When the pump is activated, the mechanism prevents the arachnoid from folding over and obstructing the suction and port, and prevents nerve roots from being sucked into the catheter. The mechanism may be an integral part of the catheter, or be operably mounted on the inner catheter wall and deployed when the needle is withdrawn.
In still another method, the distal end of the first catheter is inserted between the spinous processes of lumbar vertebrae L3 and L4 or L4 and L5 into the subarachnoid space. The distal end of the second catheter is inserted between the spinous processes of low cervical vertebrae or high thoracic vertebrae, e.g., between C-6 and C-7, between C-7 and T-1, or between T-1 and T-2, into the subarachnoid space. The CSF is aspirated preferably through the first catheter, cooled through the refrigeration system to below body temperature, and passed into the second catheter. Alternatively, the CSF is aspirated from the second catheter in the low cervical or high thoracic region and passed into the first catheter in the lumbar region to provide spinal cooling. This method may be desirable in situations where the second catheter can not be advanced rostrally in the subarachnoid space due to an edematous spinal cord after injury.
It will be understood that although the devices and methods are most useful in treating patients with spinal trauma or undergoing aortic surgery, they can be utilized to reduce neurologic damage during cerebral hypoperfusion in situations, such as cardiac arrest, cardiac failure, low cardiac output states, stroke, head injury, cerebral aneurysm surgery, open and closed cardiac surgery and aortic surgery. Selective cooling of the cerebral tissues is preferred over systemic cooling, which may have undesirable effects on the heart and other organs and induce systemic coagulopathy. In using the devices, the distal end of the first catheter is inserted between the low cervical vertebrae or high thoracic vertebrae into the subarachnoid space. The distal end of the second catheter is inserted either in the lumbar region as described above or between the cervical vertebrae, in the foramen magnum, or through a skull burr hole into the subarachnoid space or the lateral ventricle. The CSF is preferably aspirated from the first catheter in the cervical subarachnoid space, cooled to below body temperature, and passed through the second catheter into the subarachnoid space in the cervical region or the brain. The patients may be tilted back and forth to improve circulation of the hypothermic CSF in patients with stroke, head trauma, or spinal injury. The flow rate of the CSF is adjusted according to the CSF temperature and pressure to maximize hypothermic protection on the cerebral tissues.
It will be understood that there are several advantages in using the devices and methods disclosed herein for reducing neurological complications which occur during aortic surgery or trauma. For example, the devices can be used (1) to provide continuous and variable spinal cooling, (2) in patients with either blunt or penetrating spinal trauma immediately after injury, (3) to selectively provide protective hypothermia to the spinal cord, thereby avoiding complications associated with systemic cooling, (4) by an anesthesiologist prior to aortic surgery, (5) to reduce neurologic deficits during cerebral hypoperfusion in patients with, e.g., stroke, cardiac failure, or cardiac surgery, (6) during aortic surgery, such as AAA repair, to lengthen the window for reattachment of the spinal arteries, and (7) to provide intrathecal administration of neuroprotective agents.